Hi, I'm a new employee in this field so seeking for your help on solving this matter.

Currently I'm studying a DP flowmeter report about error calculation. the details are stated below:

Calibrated range: 2100 mmH2O
Flowrate : 157.57 t/hr
Accuracy : 0.035% of Span

The transmitter stability for 1 year (at operating temperature and pressure):

1 year : 1.585 mmH2O or 0.0075% of Span (which ever is higher)
Turndown ration 3:1

At 0 t/hr < Q < 52.523 t/hr:
DP reading : < 233.33 ±1.585 mmH2O
Flow reading : Q ± 4.328 t/hr (or more)

The calculation for Q is also taken at 53, 100 and 157.57 t/hr. I calculated all the said values for error and I got the same values as in the report. But for the value below the minimum flow (52.523 t/hr), I get different values which is too far from the stated values. I understand that lower flow will cause higher error percentage due to square law relationship, but i can't seem to apply it into any formula.

Thank you in advance.

 

Your accuracy value of 0.035% looks like a DP transmitter accuracy spec, which is different than the primary flow element's accuracy spec. It would highly unusual to find a DP meter run claiming 0.035% accuracy. Your report probably takes into account the combined DP and primary flow element inaccuracies.